Conventionally, a rotation angle detector has a magnet generating magnetic field and a magnetic detecting element rotating relative to the magnet for detecting a variation in magnetic field. Based on output signals of the magnetic detecting element, the detector detects the rotation angle of the detection subject.
JP-2007-256121A shows a rotation angle detector in which a magnet and a guide member are arranged in such a manner as to confront with each other so that the magnetic field is homogenized therebetween. A magnetic-field-measuring element is disposed between the magnet and the guide member. It should be noted that the guide member made of permeability material corresponds to a yoke and the magnetic-field-measuring element corresponds to a magnetic detecting element.
JP-2003-177004A (US-2003-0080732A1) shows an angle sensor in which Hall elements are arranged in such a manner as to confront a magnet through a rotational center in a cylindrical yoke, whereby linear variation in magnetic flux is enlarged.
Japanese Patent No, 4321665 (US-2004-0189288A) shows a rotation angle detector in which two magnets are arranged to confront with each other through a magnetic detecting element. Each of magnets has a curved outer surface and a curved inner surface, whereby magnetic flux passing through the magnetic detecting element is made stable.
In the detector shown in JP-2007-256121A, since there is no yoke around the magnetic-field-measuring element, the accuracy of detector is deteriorated by disturbance magnetic field. Meanwhile, in the sensor shown in JP-2003-177004A, the yoke is circumferentially provided around the Hall elements, so that the accuracy of the sensor is not always deteriorated by disturbance magnetic field. However, in this sensor, due to leakage magnetic flux, the magnetic flux vector is curved so that an area in which magnetic flux vector is uniform becomes smaller. Thus, a position of the magnetic detecting element deviates and a detection flux density changes, so that a detection error arises and “robustness” is deteriorated. That is, a system characteristic for maintaining a current condition relative to a disturbance or design error is inferior.
In the rotation angle detector shown in Japanese Patent No. 4321665, the magnetic flux vector is uniformed and “robustness” is improved. However, the shape of the magnet is complicated, which may cause an increase in manufacturing cost.